1. Field of the Invention
The present invention relates to a magnetic disk drive having a magnetic head capable of high-density writing/reading.
2. Description of the Related Art
Recently, the development of a magnetic disk drive, for increasing a recording density, is popular. In order to achieve an increase in the recording density of a magnetic disk drive, there are two possible approaches such as an increase in bit density (recording density in the disk circumferential direction) and an increase in track density (recording density in the disk radial direction). In order to achieve the techniques of these approaches, particularly, a magnetic head which remarkably improves a reproduction capability is being developed. In the development of such a magnetic head, a method is used to directly detect a medium surface magnetic field which does not depend on a relative speed, rather than the conventional method of detecting a medium surface magnetic field by electromagnetic induction which depends upon a relative speed.
A typical example of the magnetic field direct detecting method is to detect the change in resistance of a magnetoresistive (MR) element due to the strength of the medium surface magnetic field. A magnetic head employing this method is usually called an MR head. The magnetic head having separate writing and reading elements, entails the following drawbacks since there is a certain distance between both elements, i.e., magnetic gaps of both elements (meaning a center position of the effective portion of the reading element, hereinafter, referred to as merely a magnetic gap for convenience).
Many of the magnetic disk drives employ a rotary actuator for moving the magnetic head in the radial direction of the magnetic disk by rotating the arm on which the magnetic head is mounted. The rotary actuator has a simpler structure than the linear actuator, and has merits such as being vibration-proof and having low power consumption. In the case of the rotary actuator, the skew angle (created between the magnetic gap length direction of the writing/reading element and the rotating direction of a magnetic disk) is set such that it changes from the case of the inner circumference of a disk to the case of the outer circumference thereof. In the case of a magnetic head having separate writing and reading elements, an error is created in the writing track and reading track between the inner and outer circumferences of a magnetic disk with the conventional reading element arrangement. This track misregistration can be presented by D.multidot.sin .theta., when a skew angle is presented by .theta..
As a solution to the above-described drawback, the following countermeasure is proposed.
A design of such as an actuator is considered, thereby reducing the change in skew angle of the magnetic head between the innermost circumference of the magnetic disk and the outmost circumference thereof.
However, this countermeasure, when conducted along with the constant density recording method (CDR method), which can increase the recording capacity per disk about 30% as compared to the conventional method by uniforming the recording density in the inner and outer circumferences of the magnetic disk, entails the following drawback.
That is, in the case where there is no substantial difference in skew angle between the inner and outer circumferences of a magnetic disk, there is only one parameter which varies between the inner and outer circumferences, which is the radius (when the disk rotation number is constant, it is the relative speed).
In this case, it is difficult to reduce the variation of the head flying height between the inner and outer circumferences by appropriately combining the change in relative speed and the change in skew angle as in the conventional technique. Consequently, in the CDR method in which the inner and outer circumferences are divided into several zones, and the tracks of the inner to outer circumferences are set to have the same recording density as that of the tracks in the inner circumference, it is no longer possible to achieve the characteristic required for the CDR method, to uniform the head flying height (head spacing) of the inner and outer circumferences of the recording region. The minimum head flying height (set value) with which a high reliability can be obtained is determined mainly by the glide height (maximum projection height) of a magnetic disk. The glide height does not vary between the inner and outer circumferences of a magnetic disk. Therefore, when the minimum head flying height is set substantially constant between the inner and outer circumferences of the magnetic disk, substantially the same linear recording density can be achieved for both the inner and outer circumferences, making it possible to maximize the recording capacity obtained in one side of a magnetic disk while maintaining a high reliability. Thus, it is important to solve the above-described drawbacks.
As another countermeasure for track misregistration, there is a method in which the effective track width of the writing element is made wider than the effective track width of the reading element.
However, in the case where the track pitch is narrowed so as to achieve a high recording density, the track width of the reading element is remarkably narrowed, deteriorating the signal quality in terms of writing/reading characteristics. Therefore, it is not preferable to employ the above method as means for improving the real recording density.